Disc prosthesis having remote flexion/extension center of rotation

Abstract

An intervertebral disc prosthesis comprises a first endplate, a second endplate, and a bearing surface positioned between the first endplate and the second endplate. The bearing surface may be provided by a mobile bearing disc including a convex bearing surface configured to engage the first endplate and a concave bearing surface configured to engage the second endplate. The multiple bearing surfaces of the mobile bearing disc engage articulating surfaces on the endplates to form a plurality of articulating joints. Each articulating joint is configured to facilitate a particular type of movement for the segmental unit. Furthermore, each articulating joint is defined by a distinct center of rotation. The contact pair formed by the convex bearing surface of the bearing component and the concave bearing surface of the first endplate may provide a flexion/extension center of rotation for the prosthesis.

What is claimed is: 
     
       1. A disc prosthesis comprising:
 an upper endplate including a first bone contacting surface and a first articulating surface generally opposite to the first bone contacting surface; 
 a lower endplate including a second bone contacting surface and a second articulating surface generally opposite to the second bone contacting surface; and 
 a bearing component including a third convex articulating surface configured to articulate with the first articulating surface, and a fourth concave articulating surface configured to articulate with the second articulation surface, the bearing component configured such that when the disc prosthesis is implanted and viewed in cross-section in a sagittal plane, the third convex articulating surface extends from a forward non-articulating surface to a rearward non-articulating surface located at a posterior portion of the bearing component, and the entire third convex articulating surface and the entire fourth concave articulating surface continuously converge in a posterior to anterior direction, wherein the lower endplate is configured such that when the disc prosthesis is implanted and viewed in cross-section in the sagittal plane, the second articulating surface continuously diverges from the second bone contacting surface in the posterior to anterior direction. 
 
     
     
       2. The disc prosthesis of  claim 1 , the bearing component further comprising:
 a shoulder portion located posteriorly of the fourth concave articulating surface, the shoulder portion configured such that when the disc prosthesis is implanted and viewed in cross-section in the sagittal plane, the shoulder portion forms an obtuse angle with the fourth articulating surface. 
 
     
     
       3. The disc prosthesis of  claim 2 , the lower endplate further comprising:
 a flat surface located posteriorly of the second articulating surface, the flat surface configured such that when the disc prosthesis is implanted and viewed in cross-section in the sagittal plane, the flat surface extends obtusely from the second articulating surface. 
 
     
     
       4. The disc prosthesis of  claim 1 , wherein the upper endplate is configured such that when the disc prosthesis is implanted and viewed in cross-section in the sagittal plane, the first articulating surface does not continuously diverge from the first bone contacting surface in a posterior to anterior direction. 
     
     
       5. The disc prosthesis of  claim 1 , the lower endplate further comprising:
 a rail extending from a posterior portion of the second articulation surface to an anterior portion of the second articulation surface. 
 
     
     
       6. A disc prosthesis comprising:
 an upper endplate including a first bone contacting surface and a first articulating surface generally opposite to the first bone contacting surface; 
 a lower endplate including a second bone contacting surface and a second articulating surface generally opposite to the second bone contacting surface and including a forward-most portion and a rearward-most portion, the lower endplate configured such that when the disc prosthesis is implanted and viewed in cross-section in a sagittal plane, the second articulating surface extends from an anterior non-articulating surface located at the rearward-most portion of the lower endplate to a posterior non-articulating surface located at the forward-most portion of the lower endplate, and the second articulating surface continuously diverges from the second bone contacting surface in a posterior to anterior direction from the posterior non-articulating surface to the anterior non-articulating surface; and 
 a bearing component including a third convex articulating surface configured to articulate with the first articulating surface, and a fourth concave articulating surface configured to articulate with the second articulation surface, wherein the bearing component is configured such that when the disc prosthesis is implanted and viewed in cross-section in the sagittal plane, the third convex articulating surface and the fourth concave articulating surface continuously converge in the posterior to anterior direction. 
 
     
     
       7. The disc prosthesis of  claim 6 , wherein the upper endplate is configured such that when the disc prosthesis is implanted and viewed in cross-section in the sagittal plane, the first articulating surface does not continuously diverge from the first bone contacting surface in the posterior to anterior direction. 
     
     
       8. The disc prosthesis of  claim 6 , the bearing component further comprising:
 a shoulder portion located posteriorly of the fourth concave articulating surface, the shoulder portion configured such that when the disc prosthesis is implanted and viewed in cross-section in the sagittal plane, the shoulder portion forms an obtuse angle with the fourth articulating surface. 
 
     
     
       9. The disc prosthesis of  claim 8 , the lower endplate further comprising:
 a flat surface located posteriorly of the second articulating surface, the flat surface configured such that when the disc prosthesis is implanted and viewed in cross-section in the sagittal plane, the flat surface extends obtusely from the second articulating surface. 
 
     
     
       10. The disc prosthesis of  claim 6 , the lower endplate further comprising:
 a rail extending from a posterior portion of the second articulation surface to an anterior portion of the second articulation surface. 
 
     
     
       11. A disc prosthesis comprising:
 an upper endplate including a first bone contacting surface and a first articulating surface generally opposite to the first bone contacting surface; and 
 a lower endplate including a second bone contacting surface and a second articulating surface generally opposite to the second bone contacting surface, the lower endplate configured such that when the disc prosthesis is implanted and viewed in cross-section in a sagittal plane, the second articulating surface extends from a forward non-articulating surface located at an anterior location of the lower endplate to a rearward non-articulating surface, with no articulating surface of the lower endplate located anteriorly of the anterior non-articulating surface and the second articulating surface continuously diverges from the second bone contacting surface in a posterior to anterior direction from the rearward non-articulating surface to the forward non-articulating surface, wherein the lower endplate further comprises a rail extending from a posterior portion of the second articulation surface to an anterior portion of the second articulation surface. 
 
     
     
       12. The disc prosthesis of  claim 11 , further comprising:
 a bearing component including a third convex articulating surface configured to articulate with the first articulating surface, and a fourth concave articulating surface configured to articulate with the second articulation surface. 
 
     
     
       13. The disc prosthesis of  claim 11 , wherein the upper endplate is configured such that when the disc prosthesis is implanted and viewed in cross-section in the sagittal plane, the first articulating surface does not continuously diverge from the first bone contacting surface in the posterior to anterior direction.